The present invention relates to power shovels and, more particularly, to power shovels having a dipper for excavating earthen material. More specifically, the present invention relates to saddle block assemblies that support the dipper handle or arm.
There are many known earth moving apparatuses or the like. Typical prior art earth moving equipment or excavators use a bucket or dipper assembly, on the end of a movable arm, to scoop earthen material from horizontal or vertical faces. The dipper is normally provided with sharp teeth to dig against the surface being worked. The dipper further includes a cavity for collecting the material so removed. Once the earthen material is received within the dipper, the arm is typically moved to another location for transfer of the material. The material is usually discharged into a dump truck, onto a conveyor, or merely onto another pile of material.
Large electric mining rope shovels utilize a digging attachment comprising a stationary boom and a combination handle and dipper structure that mounts on the boom and that actively crowds and hoists into a bank in order to fill the dipper. As shown in FIG. 2, the handle 26 comprises two legs 68 that pass on either side of the boom 22. The handle 26 has gear racking 62 attached to the bottom of each leg 68. A shipper shaft 66 having an axis 58 is also mounted horizontally through the boom 22. Two pinions 70 with splines 74 are attached to the shipper shaft 66. The gear racking 62 on the handle legs 68 engages the pinion gear splines 74. An electric motor and a transmission (not shown) rotate the shipper shaft and pinions, thus causing the handle and racking to crowd and retract from the boom. Two saddle block assemblies 78 are mounted on the shipper shaft 66 and are used to keep the handle 26 in the proper position while the shovel is operating.
During operation the handle sees forces in the vertical and horizontal directions. The vertical force is a result of the separating force between the gear racking on the handle and the crowd pinion, and from digging loads. The horizontal force is due to the machine swinging, digging loads, and from inertia. The purpose of the saddle block assemblies is to withstand these forces and keep the handle in position.
For best operation, there should be only a small gap in between the handle and the saddle block. This gap is ideally between 0.125 inches (0.3175 centimeters) and 0.25 inches (0.635 centimeters). If the gap increases beyond this amount, the system begins to experience a couple of problems. First the gaps between the components contribute to large shock loads as the parts move. Second, a large gap on top of the handle allows the handle racking and the crowd pinion to separate from each other. This greatly increases the load on the gear teeth leading to broken gear teeth, rough operation, and increased noise.
As the saddle block assembly provides support for the handle, the handle is frequently crowding or retracting in order to dig in the bank or to swing the shovel. The relative motion between the components causes wear on the surfaces of the saddle block that are in contact with the handle. The saddle block assemblies are large structures; therefore it is not conducive to replace the entire saddle block assembly because it has wear on a couple of surfaces. For this reason, replaceable wear plates 160 form a part of the saddle block assembly. The wear plates 160 are much less expensive and easier to replace than an entire saddle block assembly. After the wear plates 160 have reached a certain thickness, they are discarded and new ones are installed. This leaves the integrity of the saddle block assemblies intact.
The saddle block wear plates 160 need to be adjusted on a regular basis to maintain the correct gap between the components. Rather than throw the wear plates 160 away at every adjustment, they are repositioned to increase their service life. Metal shims 164 and 168 are installed between the wear plates 160 and the saddle block assembly, as shown in FIG. 3, to maintain the proper operating gap. This procedure for adjusting the gap works but is time consuming and difficult. The shims are large but very thin which makes them difficult to handle. It is also awkward to work between the handle and the saddle block assembly. The area is covered in lubricant, the access is poor and the catwalks used to reach this area cannot provide ideal access to the wear plates 160. Since the wear plate adjustment is difficult, it may not be performed or it may be performed less frequently than needed.